The Evolution, Diversity and Host Associations of Rhabdoviruses
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bioRxiv preprint doi: https://doi.org/10.1101/020107; this version posted August 6, 2015. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 1 1 The evolution, diversity and host associations of rhabdoviruses 2 3 Ben Longdon1*, Gemma GR Murray1, William J Palmer1, Jonathan P Day1, Darren J 4 Parker2, 3, John J Welch1, Darren J Obbard4 and Francis M Jiggins1. 5 6 1Department of Genetics 7 University of Cambridge 8 Cambridge 9 CB2 3EH 10 UK 11 12 2 School of Biology 13 University of St. Andrews 14 St. Andrews 15 KY19 9ST 16 UK 17 18 3Department of Biological and Environmental Science, 19 University of Jyväskylä, 20 Jyväskylä, 21 Finland 22 23 4Institute of Evolutionary Biology, and Centre for Immunity Infection and Evolution 24 University of Edinburgh 25 Edinburgh 26 EH9 3JT 27 UK 28 29 *corresponding author 30 email: [email protected] 31 phone: +441223333945 32 33 bioRxiv preprint doi: https://doi.org/10.1101/020107; this version posted August 6, 2015. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 2 34 Abstract 35 36 Metagenomic studies are leading to the discovery of a hidden diversity of RNA viruses, 37 but new approaches are needed predict the host species these poorly characterised 38 viruses pose a risk to. The rhabdoviruses are a diverse family of RNA viruses that 39 includes important pathogens of humans, animals and plants. We have discovered the 40 sequences of 32 new rhabdoviruses through a combination of our own RNA sequencing 41 of insects and searching public sequence databases. Combining these with previously 42 known sequences we reconstructed the phylogeny of 195 rhabdovirus sequences 43 producing the most in depth analysis of the family to date. In most cases we know 44 nothing about the biology of the viruses beyond the host they were identified from, but 45 our dataset provides a powerful phylogenetic approach predict which are vector-borne 46 viruses and which are specific to vertebrates or arthropods. By reconstructing ancestral 47 and present host states we found that switches between major groups of hosts have 48 occurred rarely during rhabdovirus evolution. This allowed us to propose 76 new likely 49 vector-borne vertebrate viruses among viruses identified from vertebrates or biting 50 insects. Our analysis suggests it is likely there was a single origin of the plant viruses and 51 arthropod-borne vertebrate viruses while vertebrate-specific viruses arose at least 52 twice. There are also two large clades of viruses that infect insects, including the sigma 53 viruses, which are vertically transmitted. There are also few transitions between aquatic 54 and terrestrial ecosystems. Viruses also cluster together at a finer scale, with closely 55 related viruses tending to be found in closely related hosts. Our data therefore suggest 56 that throughout their evolution rhabdoviruses have occasionally made a long distance 57 host jump before spreading through related hosts in the same environment. This 58 approach offers a way to predict the most probable biology and key traits of newly 59 discovered viruses. 60 61 Keywords 62 Virus, Host shift, Arthropod, Insect, Rhabdoviridae, Mononegavirales 63 bioRxiv preprint doi: https://doi.org/10.1101/020107; this version posted August 6, 2015. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 3 64 Introduction 65 66 RNA viruses are an abundant and diverse group of pathogens. In the past, viruses were 67 typically isolated from hosts displaying symptoms of infection, before being 68 characterized morphologically and then sequenced following PCR [1, 2]. PCR-based 69 detection of novel RNA viruses is problematic as there is no single conserved region of 70 the genome of viruses from a single family, let alone all RNA viruses. High throughput 71 next generation sequencing technology has revolutionized virus discovery, allowing 72 rapid detection and sequencing of divergent virus sequences simply by sequencing total 73 RNA from infected individuals [1, 2] 74 75 One particularly diverse family of RNA viruses is the Rhabdoviridae. Rhabdoviruses are 76 negative-sense single-stranded RNA viruses in the order Mononegavirales [3]. They 77 infect an extremely broad range of hosts and have been discovered in plants, fish, 78 mammals, reptiles and a broad range of insects and other arthropods [4]. The family 79 includes important pathogens of humans and livestock. Perhaps the most well-known is 80 rabies virus, which can infect a diverse array of mammals and causes a fatal infection 81 killing 59,000 people per year with an estimated economic cost of $8.6 billion (US) [5]. 82 Other rhabdoviruses such as vesicular stomatitis virus and bovine ephemeral fever virus 83 are important pathogens of domesticated animals, whilst others are pathogens of crops 84 [3]. 85 86 Arthropods play a key role in transmission of many rhabdoviruses. Many viruses found 87 in vertebrates have also been detected in arthropods, including sandflies, mosquitoes, 88 ticks and midges [6]. The rhabdoviruses that infect plants are also often transmitted by 89 arthropods [7] and the rhabdoviruses that infect fish have the potential to be vectored 90 by ectoparasitic copepod sea-lice [8, 9]. Insects are not just mechanical vectors as 91 rhabdoviruses replicate upon infection of insect vectors [7]. Other rhabdoviruses are 92 insect-specific. In particular, the sigma viruses are a clade of vertically transmitted 93 viruses that infect dipterans and are well-studied in Drosophila [10-12]. Recently, a 94 number of rhabdoviruses have been found to be associated with a wide array of insect 95 and other arthropod species, suggesting they may be common arthropod viruses [13, 96 14]. Furthermore, a number of arthropod genomes contain integrated endogenous viral 97 elements (EVEs) with similarity to rhabdoviruses, suggesting that these species have 98 been infected with rhabdoviruses [15-18]. 99 100 Here we aimed to uncover the diversity of the rhabdoviruses, and examine how they 101 have switched between different host taxa during their evolutionary history. Insects 102 infected with rhabdoviruses commonly become paralysed on exposure to CO2 [19-21]. 103 We exploited this fact to screen field collections of flies from several continents for novel 104 rhabdoviruses that were then sequenced using RNA-sequencing (RNA-seq). Additionally 105 we searched for rhabdovirus-like sequences in publicly available RNA-seq data. We 106 identified 32 novel rhabdovirus-like sequences from a wide array of invertebrates and 107 plants, and combined them with recently discovered viruses to produce the most 108 comprehensive phylogeny of the rhabdoviruses to date. For many of the viruses we do 109 not know their true host range, so we used the phylogeny to identify a large number of bioRxiv preprint doi: https://doi.org/10.1101/020107; this version posted August 6, 2015. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 4 110 new likely vector-borne viruses and to reconstruct the evolutionary history of this 111 diverse group of viruses. 112 113 114 Methods 115 116 Discovery of new rhabdoviruses by RNA sequencing 117 118 Diptera (flies, mostly Drosophilidae) were collected in the field from Spain, USA, Kenya, 119 France, Ghana and the UK (Data S1: http://dx.doi.org/10.6084/m9.figshare.1425432). 120 Infection with rhabdoviruses can cause Drosophila and other insects to become 121 paralysed after exposure to CO2 [19-21], so we enriched our sample for infected 122 individuals by exposing them to CO2 at 12°C for 15 mins, only retaining individuals that 123 showed symptoms of paralysis 30mins later. We extracted RNA from 79 individual 124 insects (details in Data S1 http://dx.doi.org/10.6084/m9.figshare.1425432) using 125 Trizol reagent (Invitrogen) and combined the extracts into two pools (retaining non- 126 pooled individual RNA samples). RNA was then rRNA depleted with the Ribo-Zero Gold 127 kit (epicenter, USA) and used to construct Truseq total RNA libraries (Illumina). 128 Libraries were constructed and sequenced by BGI (Hong Kong) on an Illumina Hi-Seq 129 2500 (one lane, 100bp paired end reads, generating ~175 million reads). Sequences 130 were quality trimmed with Trimmomatic (v3); Illumina adapters were clipped, bases 131 were removed from the beginning and end of reads if quality dropped below a 132 threshold, sequences were trimmed if the average quality within a window fell below a 133 threshold and reads less than 20 base pairs in length were removed. We de novo 134 assembled the RNA-seq reads with Trinity (release 2013-02-25) using default settings 135 and jaccard clip option for high gene density. The assembly was then searched using 136 tblastn to identify rhabdovirus-like sequences, with known rhabdovirus coding 137 sequences as the query. Contigs with hits were then reciprocally compared to Genbank 138 cDNA and RefSeq nucleotide databases using tblastn and only retained if they hit a 139 virus-like sequence. Raw read data were deposited in the NCBI Sequence Read Archive 140 (SRP057824).